1. Field of the Invention
The invention relates to copolymers as ingredients for detergents and cleaning agents, which contain monoethylenically unsaturated mono- and dicarboxylic acids, their hydroxyalkyl esters and, if appropriate, other ethylenically unsaturated compounds as monomer units and are distinguished by a special calcium-binding and magnesium-binding capacity, detergents and cleaning agents containing these copolymers, and their use in detergents and cleaning agents, in particular as sequestering agents and antiredeposition agents.
2. Description of the Prior Art
It is known that, in addition to surfactants, so-called builders are required as ingredients in the detergent and cleaning agent industry. One of the objects of these builders is the trapping (sequestration) of cations which form water-insoluble salts, especially calcium and magnesium. These builders are therefore also referred to specifically as sequestering agents. Previously, large amounts of phosphates, especially pentasodium triphosphate, were used for this purpose. However, extremely large amounts of phosphate-containing effluents which were discharged resulted in pronounced eutrophication of bodies of water, which led to excessive growth of algae and hence to a reduction in the oxygen content of the bodies of water. Legislation in many countries is therefore directed toward the complete prohibition of phosphates or the specification of very low maximum amounts in detergents.
A large number of proposals for solving these problems have been made over the past few years. Reference may be made to the reviews in Angew. Chemie 87 (1975), pages 115-123 and in Chemikerzeitung 96 (1972), pages 685-691. According to these publications, a large number of low molecular weight and high molecular weight compounds known to be complex formers have been tested, and it has been found that polymers based on acrylic acid and derivatives of acrylic acid which contain hydroxyl groups were very suitable for partially replacing phosphates. German Laid-Open Application DOS No. 2,161,727 describes, for example, a process for the sequestration of metal ions by means of poly-.alpha.-hydroxyalkylates or their derivatives. According to Angew. Chemie, Loc. cit., such polymers have a calcium-binding capacity of 228 mg of CaO/g at 20.degree. C., and of 182 mg of CaO/g at 90.degree. C. However, a disadvantage of these compounds is that they are relatively difficult to obtain and have a relatively poor calcium-binding capacity.
German Published Application DAS No. 2,025,238 likewise discloses polymers which contain hydroxyl groups and carboxyl groups and which are obtained by so-called oxidative polymerization of acrolein, if appropriate together with acrylic acid or derivatives thereof, and subsequent treatment of the polymer or copolymer by the Cannizzaro method. In the case of these polymers too, the binding capacity does not exceed 300 mg of CaCO.sub.3 /g of active substance.
U.S. Pat. No. 4,314,044 describes a process for the preparation of relatively low molecular weight, water-soluble polymers by polymerization in aqueous solution using a special catalyst system consisting of a water-soluble initiator, a tertiary amine and a metal salt, and mentions in a general way the use of the polymers thus prepared as sequestering agents and scale inhibitors in detergents. The monomers mentioned include acrylic acid and methacrylic acid, which can be polymerized with 5 to 50% by weight of, for example, itaconic acid, maleic acid, hydroxyethyl methacrylate, hydroxypropyl methacrylate, hydroxyethyl acrylate, hydroxypropyl acrylate and other acrylyl derivatives and their mixtures. In the Examples, homopolymers and, in two cases only, binary copolymers of acrylic acid and hydroxyethyl methacrylate are described.
German Published Application DAS No. 2,616,261 describes copolymers of acrylic acid and/or methacrylic acid with hydroxyalkyl acrylates having 2 to 4 C. atoms per hydroxyalkyl group which possess a good calcium-binding capacity at room temperature. However, at temperatures of up to 95.degree. C. which prevail under the washing conditions, the calcium-binding and magnesium-binding capacities of these compounds too are inadequate by present standards.
German Laid-Open Application DOS No. 3,140,383 describes the preparation of copolymers of monocarboxylic acids, dicarboxylic acids, such as acrylic acid, methacrylic acid and maleic acid and a further monomer in an amount of 0.5 to 5% by weight, such as, for example, vinyl acetate, butyl acrylate or hydroxypropyl acrylate, and their use in detergents and cleaning agents. There is no example using hydroxypropyl acrylate. Incidentally, these copolymers too have an inadequate calcium-binding and magnesium-binding capacity, in particular at elevated temperatures.